JPS5850293B2 - Method for producing low phosphorus steel using a converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing low phosphorus steel ([P]≦0.010%) using a converter.

It is conventionally known that a double slag method is used to prevent rephosphorization when producing low phosphorus steel using the converter steel manufacturing method. However, in this conventionally known method, quicklime and fluorite are It is used as a solvent for low-temperature blowing, but it has drawbacks such as a large amount of fluorite being required because the solvent does not turn into slag due to the low-temperature blowing, and the dephosphorization reaction is also insufficient.

The present invention reduces quicklime and fluorite as solvents during primary blowing, and uses converter slag, especially high-temperature waste slag with an end point temperature of 1,650°C or higher, to promote early slag formation and removal. It has a phosphorus effect.

The high-temperature waste slag used in the present invention is 1650°C.
This is converter slag that is discharged at the above high temperature, and has a lower phosphorus content than converter slag that is discharged at a lower temperature, so there is less need to consider rephosphorus.

Generally, at the end of oxygen blowing, (P2O5)% in the slag is
and [P)% in molten steel are in a state of equilibrium, but the equilibrium constant depends on the end point temperature, and on the high temperature side, (P2O5)/CP
] decreases.

The table below illustrates the relationship between end point temperature and slag composition.

T.

Division end point temperature a0 102 205 e 1670'C 8 3 7 0,075 1,97 1640°C 7 2 0 0,068 2,46 The converter slag used in the present invention is high temperature converter slag A; When reusing it, it may be used in a molten state, or it may be cooled and solidified, then crushed and rectified to a particle size of about 5 to 100 mm.

Such high-temperature converter slag not only has the effect of promoting slag formation from the beginning of blowing until the slag formation is completed, but also allows the latent dephosphorization ability of high-temperature converter slag to be utilized. The amount of stone added can be reduced.

Next, an example of the present invention will be shown in comparison with a conventional method.

70 was charged into a converter with 95% hot metal and 5% scrap, a solvent was added, and after primary blowing, 30% was removed. When making slag steel, the conventional method is - secondary blowing process Slag secondary blowing Quicklime (kV/T) 0 0 30% Fluorite (kg/T) CP Temperature 10
2.3% 0.030% 1450°C0 0,06 0,007 1750°C Time 10 minutes 20 minutes 30 minutes In the method of the present invention, primary blowing flow Slag secondary blowing quicklime (kg/T) 0 0 30% Fluorite Converter slag (kg/T) (ky/T) 0 CP Temperature Time 2.0% 0.031% 1460°0 10 minutes 20 minutes 0.07 0.008 Results were obtained for 17500C30 minutes.

As described above, according to the present invention, low phosphorus steel of 0.010% or less can be easily produced by reducing the amount of quicklime and fluorite solvents used and effectively utilizing the high temperature converter slag, which is a waste product. The economic effect is extremely large.

In the above example, high-temperature converter slag is used as a part of the solvent, but it is also possible to use the entire amount, but in that case, the slopping phenomenon is likely to occur and there is a risk of unstable operation. Dolomite is sometimes added, but the dephosphorization effect does not change much.

Claims (1)

[Claims] 1. In manufacturing low phosphorus steel by the double slag method in the converter steel manufacturing process, part or all of converter slag, which is high temperature waste with an end point temperature of 1650°C or higher, is used as a solvent during secondary blowing. A method for manufacturing low phosphorus steel, characterized by: